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Mountain lakes are usually sensitive to the effects of global and regional environmental changes.Since the second half of the 20th century,surface-water acidification has become a significant ecological problem,and many lakes in Europe and North America have anthropogenically acidified.Additionally,following reduction in emissions of sulfur (S) and nitrogen (N) compounds,recovery from acidification has been observed in many lakes.In this study,we used changes in diatom communities to reconstruct the pH histories based on changes recorded in nine Tatra lakes (West Carpathians,Poland) since approximately 1850 AD.Overall,results indicate that acidic precipitation had little influence on lake-water pH in the Tatra Mountain lakes.Changes in diatom-inferred pH (DI-pH) generally were small and showed little evidence of acidification during the time of the highest air pollution (since the 1960s),and have shown little change since the reduction of acidic deposition since the 1990s.Lakes that showed some evidence of acidification included dystrophic lakes with low acid neutralizing capacity.However,as illustrated by the PCA trajectories of the diatom assemblages,the majority of the lakes currently contain diatom assemblages that am unlike the diatom floras that existed ca.1850.